Gas cylinder actuators generally are formed by a tubular jacket for gas containment that is closed hermetically at one end by a bottom provided with a gas filling valve and, at the opposite end, by a head portion that is provided with a hole for the passage of a stem with a piston, which translates inside said jacket; the jacket, the bottom and the head portion form the stroke compartment for the piston, while said piston, with the jacket and the bottom, forms the chamber for the compression and expansion of the gas.
These gas cylinder actuators are typically but not exclusively used for devices such as dies, molding presses and the like, in which they can be subjected to situations of high internal pressure or of impact with the associated parts of a press or of a die, such that they can be damaged; this damage can cause said gas cylinder actuator to become unusable, requiring replacement and stopping of the machine or system in which it is placed to work, but it can also be such as to harm an operator who is in the vicinity, as in the case of an explosion due to an uncontrolled pressure increase.
One of the reasons that mainly lead to such damage is what is called the overtravel of the piston, i.e., a retracting stroke of the stem with the piston that is longer than allowed from the constructive point of view for that specific gas cylinder actuator.
This overtravel can be caused for example by an unexpected increase in load on the stem of the actuator, which forces said stem to retract into the body of the actuator over an unexpected length, causing an internal overload of the actuator that can be unsustainable for the structure of the actuator as a whole.
The actuator can thus splay or break in the connecting points between the parts that compose it, or its sealing elements can fail, and in all these cases an unexpected, unwanted and dangerous rapid escape of gas can occur.
To prevent the occurrence of these dangerous overtravel situations, gas cylinder actuators have been devised which comprise safety devices designed for the controlled and safe escape of the pressurized gas in case of overtravel.
For example, granted European patent EP0959263B1 in the name of Orflam Industries, with priority dated May 22, 1998, discloses and claims a device with a compressible fluid that comprises a compression chamber that contains compressible fluid, and a piston that can be moved within said compression chamber in a first direction to compress said compressible fluid and in a second direction, which is opposite to the first one, in response to a force of the compressed fluid, the device comprising a safety element arranged so as to be struck by the piston if it performs an accidental travel that exceeds a preset nominal travel, said safety element being preset to cause the discharge of the compression chamber when struck by the piston.
A safety device for gas cylinder actuators is described and claimed in Italian patent application PD 2007 A 378 dated Nov. 13, 2007, in the name of the same Applicant as of the present application, Special Springs s.r.l.
This safety device is characterized in that it comprises, associated with the bottom or with the jacket of a gas cylinder actuator, a breakable partition that is subjected to the pressure produced by the compressed gas inside a compression and expansion chamber of a gas cylinder actuator, said breakable partition being associated with a longitudinally extending element that extends in said compression and expansion chamber over such a length as to affect part of said piston during its descent, before it performs a travel that exceeds the predefined travel (i.e., an overtravel); the longitudinally extending element is supported by flexible support means that are adapted to allow it, in the presence of a preset thrust of the piston on said longitudinally extending element, to move so as to break said breakable partition, opening an outward exit path for the gas.
Both cited safety systems for gas cylinder actuators, despite being effective, have drawbacks.
A first drawback is linked to the fact that both technical solutions provide for the breakage of a part that is designed to allow the controlled escape of pressurized gas.
Therefore, in order to restore the full functionality of said gas cylinder actuator the part needs to be replaced, consequently requiring labor as well as spare parts.
A further drawback resides in the fact that the provision of said parts preset for breaking must be extremely precise, since it is essential that these parts break exactly at the preset stress.
Otherwise, if the parts preset for breaking do not break in the presence of the design loads, or break with loads lower than the design values, the gas cylinder actuator would not be safe.
Moreover, in the cited known gas cylinder actuators, the parts designed to break in the case of overtravel are arranged inside the gas cylinder actuator and therefore any breakage thereof is not immediately visually detectable.